Susie, PPD is common in casein intolerance

especially if breast milk production was stopped abruptly. Casein is a protein found in milk. They hypothesize that the excess casein has to be reabsorbed so quickly, that more severe depression sets in. You may want to check out milk allergy. Kalle Reichelt is a researcher who has done lots of research on diet and mental status, especially related to milk and wheat. Let me know if you want more information.